"Spirit of cricket" in cricket and "unwritten rules" in baseball are both bunk as logical constructs. Both sports are hyper-competitive modern spectacles played by extremely handsomely compensated, top tier athletes looking for every edge imaginable.
The commonality between both these concepts becomes clear though when you look at the construction of the rules of each game, and the fears it leads to.
Cricket is a batsman's game, baseball is a pitcher's game. The "unwritten", and the "spirit" arbitrarily prop up pitchers and batsmen respectively, and both are slowly falling away due to any lack of logic or fairness to them. It's no coincidence it's this way.
Because the laws of cricket don't let a batsman come back in, you don't want fielding teams to just run roughshod, leading to 45, 50, 65, 32 innings totals ending early on the second day. That **** would rob the spectacle of cricket. Hence, the "spirit" favors the batsmen.
Rules of baseball don't let a pitcher come in again after being subbed ( you wouldn't really want him to anyway, but that's another story), so the big fear there is all the good pitchers get smashed out of the game, and you're left with a farcical game with sub professional level lollipop throwers in a glorified home run derby. It's happened in an All Star game before, so this isn't a crazy fear. Hence the "unwritten" favor the pitchers.
In before "walking" favors fielding sides. I'm not convinced that walking was ever a meaningful thing in competitive cricket at any levels involving umpires, much less international level. It was mostly a cudgel that you could beat the opposing side with, even though you damn well knew you and your teammates probably wouldn't do it in the biggest moments either. Thankfully walking has basically died and become irrelevant now with DRS. Current "spirit" arguments are all just about cheeky runouts now, and guess who that is favoring.